The present invention relates to electronic devices, and more particularly, to determining power quality characteristics in a power system.
Harmonic currents at frequencies other than the fundamental frequency of a power waveform can result in suboptimal performance of power system components. For example, a third harmonic current having significant energy can result in excess heating of transformers. By determining the harmonic content of a power waveform, undesirable harmonics can be filtered out and/or otherwise accommodated for in a power system.
In some instances, the total harmonic content can be determined as the total harmonic distortion (THD) of a waveform. The THD can be computed using a Discrete Fourier Transform (DFT) or a Fast Fourier Transform (FFT). When computing a THD of a waveform, the waveform may be sampled periodically N times. When computing a DFT, 2N2 calculations may be required. Similarly, the FFT may require 2N log N calculations. Storing the results of such calculations may require substantial storage resources, such as for example, large blocks of memory.
Typically, the output of a DFT consists of bins that include magnitude and phase data for different frequencies. In order to compute THD from, for example, a DFT, an additional complex calculation on the array of the frequency domain data is typically performed. Selection of optimal sampling parameters in bandwidth processing gain and spectral leakage in consecutive bins can be computed using Nyquist criteria. For example, in the case of a sixty Hertz waveform, as frequently utilized in power applications, a desirable number of computed samples may be 2048. Thus, the number of calculations for computing a power waveform property may require significant memory and processing resources. A more efficient technique for performing harmonic analysis of a power waveform is desired.